A tape medium is used as a storage device capable of reading/writing large amounts of data sequentially at low cost. It is important for the entire storage system including a tape drive to finish backup and recovery of the large amounts of data within a certain amount of time.
Writing data from a host results in accumulation of data in a buffer memory (also called a buffer) inside a tape drive. When the write speed (drive transfer speed or drive transfer rate) to a tape on the drive side is faster than the data writing speed (host transfer speed or host transfer rate) on the host side, the buffer memory is emptied of data. When the buffer memory gets empty, the tape drive usually performs processing, called a back hitch, for rewinding the recording medium. The back hitch requires a few seconds (3 or 5 seconds). During the back-hitch rewinding operation, the tape drive writes data to the tape medium and no data can be read into the buffer. Since the back hitch operation keeps data transfer from the host waiting, the data transfer rate is affected as a whole. On the other hand, during data reading from the host, the tape drive performs a back hitch when the buffer memory becomes full of data.